We propose to purchase a three-laser Canto II research-only cell analyzer made by Becton, Dickinson and Company for the Stanford Shared FACS Facility. This system, which is capable of measuring two light scatter signals and up to eight fluorescence signals, will replace an analyzer custom built by Facility staff in 2000. The custom-built instrument now serves approximately 120 users from 35 different research labs at Stanford. The old analyzer is becoming increasingly difficult to maintain, in part due to difficulties in obtaining replacement parts, and poses an unacceptable risk of failure for ongoing experiments. Purchase of a new instrument will insure that Shared FACS Facility users have access to this critical instrumentation. The new purchase will not result in an increase in recharge rates to these users. The Canto II has a number of capabilities that are not available on the instrument to be replaced. These include two additional fluorescence parameters, 562-nm laser excitation, and a 96-well plate reader. These additions will allow current users enhanced flexibility in planning experiments and will provide current users of the Facility's high-end LSR-II analyzer the option of using a less-expensive instrument. The Shared FACS Facility staff has extensive experience with the software and electronics used in the Canto and should have no difficulties integrating it into the Facility and training the existing user base, as well as new users, in its operation. Almost all the work done in the Stanford Shared FACS Facility is health-related research, ranging from basic studies in molecular biology, genetics, and development to clinical research on AIDS and other diseases. The large majority of the work in the Facility is NIH supported.